Dusty was helping Twilight with a experiment since Spike was gone with Rarity to go Gem Hunting and Starlight was Sick, Dusty was available since he had nothing to do and helping Twilight would be interesting for him.

But what happened next was shocking as Dusty was exposed to whatever was contained inside of the potion which caused him to shrink down to the size of a Breezie and Twilight needs to find somepony to care for him while she looks for way to cure this.

Cover is made by Jeroen01 from DA